The objectives of this project were: a) to understand the basic biosynthetic process of opioid and tachykinin systems by employing molecular biology and immunochemical techniques, b) to elucidate how the classical neurotransmitter systems such as dopamine (DA) interact with neuropeptide systems, c) to understand whether pharmacological agents such as haloperidol, lithium, apomorphine or physiological stress, such as insulin-shock, would perturb the biosynthetic processes of neuropeptides. The methods to study the biosynthetic steps include the quantitation of specific mRNAs, measurement of the precursor content as well as the steady-state peptide concentration. Long-term blockade of DA receptors with DA antagonist haloperidol (an antipsychotic drug) or specific lesion of DA neurons leads to an increase in the expression of Met5-enkephalin (ME) biosynthetic process. This finding not only suggests the physiological regulation of metabolism of the ME system by the DA system but also raises important concept that gene expression of neuropeptide systems may be an important site of action for antipsychotic drugs. Further, these results may also have relevance to the adaptive processes in the pathological states such as Parkinson's disease and Lesch-Nyhan syndrome. Apomorphine, a dopamine agonist induced a selective increase in dynorphin (DY) level which could be blocked by haloperidol; the latter drug on the other hand, increases ME level without affecting DY level. These results demonstrate a reciprocal regulation of ME and DY systems by DA system. The antimanic drug lithium appears to increase the gene expression of ME, DY as well as substance P systems. This suggests that lithium may stimulate genetic expression by a common mechanism at the transcription level. These and other in vitro studies with adrenal chromaffin cells provide a strategy to determine the dynamic state of a given neuropeptide system. In conclusion, the approaches used not only provide information on the biosynthetic pathways of neuropeptide systems and their interactions with neurotransmitter systems, but also gives impetus to the development of new strategies for pharmacological manipulation of pathological states.